Maybe your classes were different. Way back when I was in school, if you missed the final exam of a class for a reason that wasn't excused, you did not make up the exam. You got a zero, and if that exam was weighted enough and/or your other grades in the class weren't high enough, you'd fail the class. Illness with a doctor's note or death in the family were good reasons to make up the final. A sporting event would not have been.
Most directors say nothing is excused. My son's director last year said that. It was listed in the handbook. But when my son had to miss a required competition which was a huge part of his semester grade because my father had just died of cancer, the director told us how sorry he was and said not to worry about the grade, of course my son could do something else to make up that grade. Would he have done that if my son chose to miss the concert for a game of some sort? I seriously doubt it, especially since my son had a solo and they had to scramble to assign it to someone else. Despite what you seem to think, band directors are not crazed dictators. They are reasonable people. But in the end all that matters is that you don't have to be in band. If you aren't willing to put in the work and meet the requirements of the class, don't enroll in the class. It's simple.